1) All the way 2) Earnestly or intently 3) English surname 4) Getting it on demand 5) Higher on the mohs scale 6) Indulging excessively 7) Into a solid condition 8) Less cushiony 9) Less giving 10) Less simple 11) More arduous 12) More backbreaking 13) More challenging 14) More demanding 15) More difficult Found on https://www.crosswordclues.com/clue/harder
The USS Harder was an American Gato Class submarine of 1525 tons displacement launched in 1942 and lost during the Second World War. The USS Harder had a top speed of 21 knots surfaced and carried a complement of between 65 and 74. She was armed with one 3 inch dual-purpose gun; two 20 mm Oerlikon anti-aircraft guns; six 21 inch bow torpedo tubes a... Found on http://www.probertencyclopaedia.com/browse/RH.HTM